The proposed research will continue studies of the role of calcium ions in the alpha-adrenergic activation of glycogen breakdown by catecholamines in isolated liver cells. Experiments will be designed to test the hypothesis that activation of alpha-adrenergic receptors causes release of Ca2 ions from intracellular stores and that the resulting increase in cytoplasmic Ca2 ions concentration causes activation of phosphorylase through stimulation of phosphorylase kinase. They will involve: a. Measurements of intracellular phosphorylation of phosphorylase by incubating hepatocytes with 32P-inorganic phosphate and isolating labelled phosphorylase by immunoprecipitation. b. Attempts to measure changes in cytoplasmic Ca2 ions using arsenazo III. c. Identification of the site(s) from which calcium is mobilized using electron microscopic studies with pyroantimonate, chlorotetra-cycline fluorescence studies, subcellular fractionation techniques, and 45Ca binding studies with plasma membranes, mitochondria and microsomes. d. Attempts to determine the mechanism(s) by which alpha-adrenergic activation mobilizes intracellular Ca2 ions.